Tests detected toxic substances in soil, water and ash samples taken from residents' property miles away from a chemical plant that flooded during Hurricane Harvey, it is alleged.

The 15 residents named as plaintiffs link the toxins to products stored or made at Arkema Inc.'s facility in Crosby, about 25 miles (40 kilometres ) northeast of Houston, Texas, and say the releases violated environmental protection laws.

The residents blame Arkema and its France-based parent company for failing to take more precautions to control flooding - the plant is in a government-designated flood plain - and to fully warn them about the health risks of smoke and water from the site.

According to the lawsuit, one woman's two daughters had respiratory trouble and headaches after moving back into their home, where the toxins were found.

Another plaintiff, Shannan Wheeler, told AP that he found gooey black deposits in his flower beds and developed a thick, scaly rash while picking up grass clippings after mowing following the fire at the plant.

"The third or fourth scoopful, I noticed the stinging, the tingling," said Ms Wheeler, noting that his doctor told him scarring was likely.

"The next one was like, 'Damn it.' I thought I'd gotten in ants. It started getting red. I kept picking up. After two more, I said that's enough, something's wrong here."

In a written statement, Arkema said it has not detected chemicals in off-site sampling that exceeds levels for clean-up set by the state's environmental agency.

"We don't know what these lawyers tested for," the company wrote, saying that it wouldn't comment further on the lawsuit.

The company has previously declined to say which chemicals were released during the fire or discuss how large its inventory quantities were prior to the incident.

It provided only the names of its chemicals on its website last month after days of public pressure.

As Harvey dumped the rain, Arkema's power and generators at its Crosby facility failed, leading refrigeration systems to shut down.

That caused its organic peroxides, used in a range of products from plastics and paints, to destabilise.

Arkema abandoned the facility on August 29 after, executives have said, as much as six feet (1.8 metres) engulfed it. A mandatory 1.5-mile (2.4-kilometre) evacuation zone was created in anticipation of a fire and explosion, displacing hundreds of residents for about a week.

After one container storing hazardous materials caught fire on August 31 and exploded, an Arkema executive claimed that smoke from that was a "non-toxic irritant." Fifteen responders were treated for exposure at local hospitals.

On September 4, after a second container caught fire and then the remaining others were burned under supervision, an executive said Arkema's air-quality testing within the evacuation zone had shown "no evidence of any issues".

But the class-action lawsuit, filed in a Houston federal court, said several residents had found "strange black ash" and "black residue" on the ground after each Arkema explosion sent plumes of smoke in the air.